selftests: net: fib_rule_tests: fix support for running individual tests

parsing and usage of -t got missed in the previous patch.
this patch fixes it

Fixes: 816cda9ae531 ("selftests: net: fib_rule_tests: add support to select a test to run")
Signed-off-by: Alaa Mohamed <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/net/fib_rule_tests.sh

···
 	log_section "IPv6 fib rule"
 	fib_rule6_test
 }
+################################################################################
+# usage
+
+usage()
+{
+	cat <<EOF
+usage: ${0##*/} OPTS
+
+        -t <test>   Test(s) to run (default: all)
+                    (options: $TESTS)
+EOF
+}
+
+################################################################################
+# main
+
+while getopts ":t:h" opt; do
+	case $opt in
+		t) TESTS=$OPTARG;;
+		h) usage; exit 0;;
+		*) usage; exit 1;;
+	esac
+done
 
 if [ "$(id -u)" -ne 0 ];then
 	echo "SKIP: Need root privileges"